Polypropylene resins are used to make nonwoven fabrics for applications such as diaper liners, medical gowns, and oil absorbents. One of the most important properties of these materials is their strength. For making conventional spunbonded materials, relatively high melt flow rate (MFR) resins (lower viscosity or lower molecular weight) are used at relatively low spinning temperatures, even though lower MFR (higher viscosity or higher molecular weight) resins give greater fabric strength. If a low MFR resin is employed, it cannot be processed at a normal spinning temperature because too many spin breaks occur. Spunbond fiber resins currently used have a MFR of about 40 and adequate spin continuity is maintained at a spinning temperature of about 210.degree. C.
Various combinations of stabilizers have been used to prevent thermal degradation of polyolefins, as well as to increase resistance to degradation by light and to improve processability. Japanese published application 61-133251 discloses a heat resistant polyolefin resin molding composition containing a combination of a phenolic antioxidant, an organic phosphite, and hydrotalcite. U.S. Pat. No. 4, 611,024 discloses an injection molding grade resin that can also be used for making fibers and films. The resin contains an acetal clarifying agent and hydrotalcite. Optional ingredients include a phenolic antioxidant, an organic phosphite and a metal soap such as calcium stearate. U.S. Pat No. 4,965,301 discloses a stabilizer package for polyolefin fibers comprising (a) at least one hindered phenol, (b) at least one organic phosphite, (c) at least one hindered amine, (d) at least one metal salt of a long chain fatty acid, and (e) an alkali metal phosphate. U.S. Pat. No. 5,246,777 discloses a fiber-forming polyolefin composition stabilized against heat, oxidation, light, and discoloration by combustion gases. The stabilizers include a hindered phenol, a hindered piperidine compound, and, optionally, an organic phosphorus compound antioxidant. Thus there is a need for a combination of additives that will provide spunbonded materials with increased tensile strength.